#include <stdio.h>

double CancelFee(double price);

int main(int argc, char *argv[]) {

    double pay=0;
    scanf("%lf", &pay);
    printf("%.1f", CancelFee(pay));
    return 0;
}

double CancelFee(double price){
    double r = price * 0.05;
    int k = r;
    double l = r - k;

    double damages = 0.0;
    if(l<0.25)
        return damages=k;
    else if(l>=0.25&&l<0.75)
        return damages = k + 0.5;
    else if(l>=0.75&&l<1)
        return damages = k + 1;
    else
        return 0;
}